title: Physiological correlates of endurance time variability during constant-workrate cycling exercise in patients with COPD.
abstract: BACKGROUND
  The endurance time (T(end)) during constant-workrate cycling exercise (CET) is highly variable in COPD. We investigated pulmonary and physiological variables that may contribute to these variations in T(end).
  
  
  METHODS
  Ninety-two patients with COPD completed a CET performed at 80% of peak workrate capacity (W(peak)). Patients were divided into tertiles of T(end) [Group 1: <4 min; Group 2: 4-6 min; Group 3: >6 min]. Disease severity (FEV(1)), aerobic fitness (W(peak), peak oxygen consumption [VO2(peak)], ventilatory threshold [VO2(VT)]), quadriceps strength (MVC), symptom scores at the end of CET and exercise intensity during CET (heart rate at the end of CET to heart rate at peak incremental exercise ratio [HR(CET)/HR(peak)]) were analyzed as potential variables influencing T(end).
  
  
  RESULTS
  W(peak), VO2(peak), VO2(VT), MVC, leg fatigue at end of CET, and HR(CET)/HR(peak) were lower in group 1 than in group 2 or 3 (p≤0.05). VO2(VT) and leg fatigue at end of CET independently predicted T(end) in multiple regression analysis (r = 0.50, p = 0.001).
  
  
  CONCLUSIONS
  T(end) was independently related to the aerobic fitness and to tolerance to leg fatigue at the end of exercise. A large fraction of the variability in T(end) was not explained by the physiological parameters assessed in the present study. Individualization of exercise intensity during CET should help in reducing variations in T(end) among patients with COPD.
authors.affiliation: Centre de Recherche, Institut Universitaire de Cardiologie et de Pneumologie de Québec, Université Laval, Québec, Canada.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Vivodtzev
authors.forename: Philippe
authors.initials: P
authors.lastname: Gagnon
authors.forename: Véronique
authors.initials: V
authors.lastname: Pepin
authors.forename: Didier
authors.initials: D
authors.lastname: Saey
authors.forename: Louis
authors.initials: L
authors.lastname: Laviolette
authors.forename: Cynthia
authors.initials: C
authors.lastname: Brouillard
authors.forename: François
authors.initials: F
authors.lastname: Maltais
mesh_terms: D000368:Aged; D001642:Bicycling / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test / Q000379:methods*; D017079:Exercise Tolerance / Q000502:physiology; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D007206:Individuality; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption / Q000502:physiology; D010807:Physical Endurance / Q000502:physiology*; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology*; D012129:Respiratory Function Tests; D013997:Time Factors